Preparation method and application of apple leaf extract and metal preservative

Abstract

The invention discloses a preparation method and application of an apple leaf extract and a metal corrosion inhibitor. The preparation method comprises the following steps: drying fresh apple leaves, crushing and sieving to obtain apple leaf powder, mixing the apple leaf powder with water, heating, filtering, and freeze-drying filtrate to obtain the apple leaf extract. According to the apple leaf extract provided by the invention, a good corrosion inhibition effect can be achieved in five systems of Cu in a 0.5 M H2SO4 solution, Q235 in the 0.5 M H2SO4 solution, Q235 in a 1 M HCl solution, N80 in the 1 M HCl solution and X80 in the 1 M HCl solution.

Description

Technical Field

[0001] The present invention relates to the field of metal material corrosion prevention, and in particular to a preparation method and application of an apple leaf extract and a metal corrosion inhibitor. Background Art

[0002] Driven by social and economic development, the demand for metal materials is increasing across various fields. Carbon steel, due to its high strength and low cost, is widely used in building frames, mechanical parts, pipelines, and industrial equipment. Copper, due to its excellent electrical and thermal conductivity and plasticity, is widely used in electrical, medical, and heat exchange equipment. However, acid-driven corrosion is one of the greatest challenges facing many metals. For example, pickling processes during metal surface treatment, acidic substances in industrial equipment and pipelines, and acidic gases in air conditioning systems and automotive exhaust systems can all cause severe corrosion of the metal matrix. As an effective means of metal corrosion prevention, corrosion inhibitors occupy a key position among various anti-corrosion methods due to their simplicity, low dosage, low cost, and significant effectiveness. To date, researchers at home and abroad have developed a variety of highly effective corrosion inhibitors, including inorganic inhibitors such as chromates and phosphates, and organic inhibitors such as benzothiazole and molecules rich in heteroatoms (S, N, O). However, many traditional organic and inorganic inhibitors, such as certain organic amines and heavy metal compounds, can be toxic and harmful to soil, water, and human health. With the global promotion of green chemistry and sustainable development goals, countries have gradually imposed restrictions on traditional corrosion inhibitors. The development of environmentally friendly, sustainable, economical and multifunctional corrosion inhibitors has become an important development direction in this field. Summary of the Invention

[0003] The present invention aims to overcome the problem that existing corrosion inhibitors cannot meet environmental protection requirements and provide a preparation method and application of apple leaf extract and a metal preservative. The apple leaf extract corrosion inhibitor provided by the present invention has good slow-release performance for various metals such as carbon steel and copper in different media environments.

[0004] In order to achieve the above-mentioned objectives, the first aspect of the present invention provides a method for preparing apple leaf extract, wherein the preparation method comprises the following steps: drying fresh apple leaves, crushing and sieving to obtain apple leaf powder, mixing the apple leaf powder with water, heating, filtering, and freeze-drying the filtrate to obtain apple leaf extract.

[0005] The second aspect of the present invention provides a use of the apple leaf extract prepared by the preparation method described in the first aspect of the present invention as a corrosion inhibitor.

[0006] The third aspect of the present invention provides a metal preservative, wherein the metal preservative comprises a solvent and an additive, wherein the solvent comprises ethyl lactate and ethanol, and the additive comprises apple leaf extract and polylactic acid-glycolic acid copolymer.

[0007] Apple leaves are rich in polyphenolic compounds such as chlorogenic acid and gallic acid. These substances can adsorb onto metal surfaces to form a protective film, effectively inhibiting corrosion reactions. Polyphenolic compounds also have strong antioxidant properties, which can further slow the rate of metal oxidation. In addition, apple leaves also contain flavonoids such as quercetin and kaempferol, which can effectively protect metal surfaces by chelating metal ions and preventing corrosion reactions.

[0008] While conventional corrosion inhibitors typically only have an anti-corrosion effect on a single medium, the multifunctional corrosion inhibitor proposed in this paper, using apple leaf extract as its primary ingredient, exhibits broader anti-corrosion applicability. Apple leaves are rich in a variety of active ingredients, enabling the inhibitor to not only inhibit the corrosion of a single material but also demonstrate excellent applicability across diverse media environments.

[0009] The apple leaf extract provided by the present invention can ensure that Cu has good corrosion inhibition effects in five systems: 0.5M H2SO4 solution, Q235 in 0.5M H2SO4 solution, Q235 in 1M HCl solution, N80 in 1M HCl solution, and X80 steel in 1M HCl solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is an infrared spectrum of the apple leaf extract prepared in Example 1;

[0011] Figure 2 The Nyquist plot, potentiodynamic polarization curve, and scanning electron micrographs of Cu before and after immersion are for the Cu-0.5M H2SO4 solution system.

[0012] Figure 3 The Nyquist plot, potentiodynamic polarization curve, and scanning electron micrographs of Q235 steel before and after immersion in the Q235-0.5M H2SO4 solution system are shown.

[0013] Figure 4 The Nyquist plot, potentiodynamic polarization curve, and scanning electron micrographs of Q235 steel before and after immersion in 1 M HCl solution are shown.

[0014] Figure 5 The Nyquist plot, potentiodynamic polarization curve, and scanning electron micrographs of N80 steel before and after immersion in N80-1 M HCl solution are shown.

[0015] Figure 6The Nyquist plot, potentiodynamic polarization curve, and scanning electron micrographs of X80 steel before and after immersion in the X80-1 M HCl solution system are shown.

[0016] Figure 7 This is a partial schematic diagram of the V-groove of the X80 steel butt joint. DETAILED DESCRIPTION

[0017] The following detailed description of the specific embodiments of the present invention is provided in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are intended only to illustrate and explain the present invention and are not intended to limit the present invention. In the description of this specification, reference to the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine different embodiments or examples and features of different embodiments or examples described in this specification without conflict. The endpoints and any values ​​of the ranges disclosed herein are not limited to the exact ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the values ​​between the endpoints of each range, between the endpoints of each range and individual point values, and between individual point values ​​can be combined to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein. In addition, the term "and / or" in the specification and claims is used to describe an association relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0018] A first aspect of the present invention provides a method for preparing apple leaf extract, which comprises the following steps: drying fresh apple leaves, crushing and sieving them to obtain apple leaf powder, mixing the apple leaf powder with water, heating it, filtering it, and freeze-drying the filtrate to obtain the apple leaf extract.

[0019] Preferably, the mass-to-volume ratio of the apple leaf powder to water is 2-3:100. The mass-to-volume ratio of apple leaf powder to water directly affects the concentration of the extract, and thus the corrosion inhibition effect. When the mass ratio of the two is less than the preset range, there is still room for dissolution, and the extraction rate is insufficient. When it is greater than the preset range, the powder cannot be effectively dissolved, resulting in a waste of resources. The mass-to-volume ratio of apple leaf powder to water can be 2g:100mL, 2.2g:100mL, 2.5g:100mL, 2.7g:100mL, 3g:100mL, and any value between any two of them.

[0020] Preferably, the heating temperature is 333-343K, and the heating time is 2-3 hours. When the temperature is lower than 333K, the powder dissolves more slowly, and the complete dissolution process takes more time, resulting in a prolonged reaction time. When the temperature is higher than 343K, the amount of water evaporated from the mixed solution increases, resulting in a decrease in the amount of dissolved powder. The heating temperature can be 333K, 335K, 337K, 340K, 343K, or any value between any two of these numbers. The heating time can be 2 hours, 2.5 hours, 3 hours, or any value between any two of these numbers.

[0021] Preferably, the drying temperature is 323-333 K and the drying time is 36-48 h. If the drying temperature is too high, the sample may be at risk of carbonization. If the drying time is too short, the moisture in the sample cannot be completely removed, which will make the subsequent crushing process difficult. The drying temperature can be 323 K, 328 K, 330 K, 333 K, or any value between any two of these numbers. The drying time can be 36 h, 40 h, 44 h, 48 h, or any value between any two of these numbers.

[0022] Preferably, the filtrate is frozen before freeze-drying, and the freezing temperature is 255-260 K and the time is 12-24 hours. The purpose of freezing is to convert the liquid substance into a solid state, which facilitates the subsequent freeze-drying.

[0023] Preferably, the sieve aperture is 1-1.5 mm.

[0024] Preferably, the freeze-drying time is 24-36 hours.

[0025] The second aspect of the present invention provides a use of the apple leaf extract prepared by the preparation method described in the first aspect of the present invention as a corrosion inhibitor.

[0026] Preferably, the corrosion inhibitor is suitable for corrosion protection of metallic copper and / or carbon steel in acidic medium.

[0027] Preferably, the acidic medium comprises a sulfuric acid solution and / or a hydrochloric acid solution, and the concentration of the acidic medium is 0.5-1M.

[0028] The third aspect of the present invention provides a metal preservative, wherein the metal preservative comprises a solvent and an additive, wherein the solvent comprises ethyl lactate and ethanol, and the additive comprises apple leaf extract and polylactic acid-glycolic acid copolymer.

[0029] Combine Figure 7 As shown, some pipe sections 1 to be welded (made of X80 steel) are processed with V-grooves 2 on their slopes. The width of the V-grooves 2 is no more than 2 mm, the depth is no more than 2 mm, and the spacing between adjacent V-grooves 2 is no more than 5 mm. Commonly used slope shapes include X-grooves, V-grooves, and U-grooves. Generally, after the pipe sections 1 to be welded are processed in the workshop, before the two pipe sections 1 are transported to the construction site for welding, it is necessary to apply an anti-corrosion coating on the slope to prevent corrosion and rust on the grooves, which affect the welding quality. For pipe sections 1 with V-grooves 2 on their slopes, since the V-grooves 2 are numerous and small, and the bottom of the grooves is very narrow, when applying conventional anti-corrosion coatings (such as epoxy anti-corrosion paint), the bottom of the V-grooves 2 often has residual air, resulting in inadequate coating and bubbles, which leads to unqualified subsequent welding. The use of the metal preservative provided by the present invention can effectively avoid this disadvantage. This is because the metal preservative provided by the present invention contains apple leaf extract and polylactic acid-glycolic acid copolymer, which can form a tightly fitting film on the metal surface and the surface of the V-shaped groove 2, and has an excellent anti-corrosion effect, especially on the microstructure of the metal surface. It has excellent wetting performance and can effectively improve the welding quality of the weld slope with microstructure.

[0030] Preferably, the volume ratio of the ethyl lactate to the ethanol is 85-90:10-15, the concentration of the apple leaf extract is 200-600 mg / L, preferably 400-600 mg / L, based on the total amount of the solvent, and the concentration of the poly(lactic-co-glycolic acid) copolymer is 5-20 w / v. The concentration of the poly(lactic-co-glycolic acid) copolymer is 5-20 w / v, i.e., 5 g, 10 g, 15 g, 20 g, etc. of the poly(lactic-co-glycolic acid) copolymer is contained in every 100 ml of solvent.

[0031] Preferably, the weight average molecular weight of the polylactic acid-glycolic acid copolymer is 1000-4000.

[0032] Compared to traditional organic and inorganic corrosion inhibitors, apple leaves, as an agricultural byproduct, do not rely on chemical synthesis, avoiding the production of toxic and hazardous substances. This promotes the transition of corrosion inhibitors from chemical synthesis to natural, green materials. Apple leaves, a common waste from agricultural pruning and processing, are often discarded or incinerated and underutilized. However, using apple leaf extract in the preparation of corrosion inhibitors can give them new economic value, embodying the concept of waste resource utilization and providing a new solution for the development of agricultural waste.

[0033] Apple leaves are rich in polyphenols and flavonoids, active ingredients that significantly inhibit metal oxidation. They can form chemical bonds with metal surfaces and generate stable protective films through adsorption, providing new materials for more efficient and multifunctional corrosion inhibitors. The development and promotion of corrosion inhibitors containing apple leaf extracts will not only achieve technological breakthroughs in metal corrosion protection but also provide effective solutions for the comprehensive utilization and sustainable development of agricultural waste, possessing significant scientific research and industrial promotion value.

[0034] The present invention will be further described below with reference to specific embodiments.

[0035] The metal materials used in the following examples and comparative examples include copper (purity 99.9%), and carbon steels include Q235, N80, and X80, all of which are commercially available and cut into several 1 cm × 1 cm × 1 cm sheets for later use.

[0036] The weight average molecular weight of the polylactic acid-glycolic acid copolymer is 2000.

[0037] Preparation of working electrodes in electrochemical tests: Prepared copper sheets, Q235 steel sheets, N80 steel sheets and X80 steel sheets were placed on the working area (working area of ​​1 × 1 cm 2 ) are sealed and cured with epoxy resin to make working electrodes.

[0038] Example 1

[0039] Fresh apple leaves were washed with ultrapure water, then placed in an oven and dried at 330K for 40 hours. After the apple leaves were completely dried, they were placed in a grinder and crushed to obtain a coarse powder, which was then sieved with a 1.25mm pore size sieve to obtain fine apple leaf powder. 25g of the obtained apple leaf powder was added to 1L of ultrapure water, heated to 340K, and stirred with a magnetic stirrer at 400rpm for 2.5h. The mixed solution was passed through a vacuum filtration device to remove the apple leaf residue to obtain a transparent filtrate. The transparent filtrate was placed in a refrigerator and frozen at 258K for 16h, then placed in a vacuum freeze dryer and freeze-dried for 30h. After complete drying, the apple leaf extract was obtained.

[0040] The infrared spectrum of the prepared apple leaf extract is as follows Figure 1 As shown, at 3426.85cm -1 A significant broad peak appears at 2925.09 cm, which is due to the stretching vibration of OH or NH bonds. -1 The peak at 1621.75cm indicates the presence of a CH bond. -1 The peak at 1403.51cm is the stretching vibration of C=O or C=C bond. -1The absorption peak at 1077.16 cm is attributed to the stretching vibration of the CN bond. -1 The absorption peak at is derived from the stretching vibration of CO. -1 Numerous peaks appeared at the position of , confirming the presence of CH groups. During the action of corrosion inhibitors, their N, O, S, and other related functional groups typically form chemical bonds with metal surfaces, leading to adsorption. Therefore, substances containing a certain amount of N, O, and S are considered to have potential as corrosion inhibitors. The apple leaf extract prepared in this invention contains O and N related functional groups, demonstrating its potential for inhibiting metals from corrosion.

[0041] A series of sulfuric acid test solutions containing apple leaf extract were prepared. The concentrations of the apple leaf extract in the series of sulfuric acid test solutions were 0, 100, 200, 400, and 600 mg / L, respectively, and the solvent was a 0.5 M sulfuric acid solution.

[0042] A series of hydrochloric acid test solutions containing apple leaf extract were prepared. The concentrations of the apple leaf extract in the series of hydrochloric acid test solutions were 0, 100, 200, 400, and 600 mg / L, respectively. The solvent was a 1 M sulfuric acid solution.

[0043] Test Example 1 Electrochemical Test

[0044] The test was performed on a Gamry Reference 600+ electrochemical workstation using a classic three-electrode system, with the treated Q235 steel, N80 steel, X80 steel, and copper as working electrodes, and a 1 cm 2 A platinum sheet was used as the counter electrode, and saturated calomel was used as the reference electrode. Before each experiment, the working electrode was polished with a series of sandpapers of different grades (400#, 800#, 1200#, 2000#), washed with distilled water, and degreased with acetone.

[0045] The test was conducted at 298K, with each working electrode immersed in the corresponding test solution, and then electrochemical impedance spectroscopy (EIS) and polarization curve (PD) tests were performed. In the AC impedance test (EIS), the AC wave amplitude was 5mV, and the scanning frequency range was 105Hz-10-2Hz. The experimental data were fitted using ZSimpWin software. In the potentiodynamic polarization curve (PD) test, the scan rate was 1mV / s, and the potential range was ±250mV relative to the open circuit potential.

[0046] Among them, each working electrode and the corresponding test solution are as follows:

[0047] The Cu working electrode was immersed in a series of sulfuric acid test solutions for 1800s to obtain a stable open circuit potential; the Q235 steel working electrode was immersed in a series of sulfuric acid test solutions for 1800s to obtain a stable open circuit potential; the Q235 steel working electrode was immersed in a series of hydrochloric acid test solutions for 1800s to obtain a stable open circuit potential; the N80 steel working electrode was immersed in a series of hydrochloric acid test solutions for 1800s to obtain a stable open circuit potential; the X80 steel working electrode was immersed in a series of hydrochloric acid test solutions for 1800s to obtain a stable open circuit potential.

[0048] Test Example 2 Surface morphology observation

[0049] The surface morphology of Q235 steel, N80 steel, X80 steel, and copper was analyzed using a field-emission scanning electron microscope (ZEISSMERLIN COMPACT). Before testing, the surfaces of the Q235, N80, X80, and copper sheets were polished sequentially with 500- to 5000-grit aqueous sandpaper to a mirror finish on all six sides. The surfaces were then ultrasonically cleaned in distilled water and anhydrous ethanol for 2 minutes. The following five experimental systems were conducted at 298 K.

[0050] In the Cu sheet-0.5M H2SO4 solution system: the copper sheet was immersed in sulfuric acid corrosion medium without adding apple leaf extract and containing 600 mg / L apple leaf extract for 48 hours.

[0051] In the Q235-0.5M H2SO4 solution system: Q235 steel sheets were immersed in sulfuric acid corrosion media without apple leaf extract and containing 600 mg / L apple leaf extract for 6 hours.

[0052] Q235 steel sheet, N80 steel sheet, and X80 steel sheet were immersed in 1M HCl solution without apple leaf extract and in 1M HCl solution containing 600 mg / L apple leaf extract for 6 h, respectively.

[0053] After the above immersion test is completed, deionized water and anhydrous ethanol are used for ultrasonication in sequence, and then air-dried with cold air for testing.

[0054] The test results are analyzed as follows:

[0055] (1) Test results of Cu-0.5M H2SO4 solution

[0056] The obtained Nyquist plot is as follows Figure 2 As shown in (a), the impedance data of different concentrations of apple leaf extract were fitted by Zsimpwin software to obtain a series of electrochemical parameters. The experimental results show that in the blank solution without apple leaf extract, the polarization resistance is 503.4Ωcm 2When the concentration of apple leaf extract is 100 mg / L, the polarization resistance is 2412 Ωcm 2 , the corrosion inhibition efficiency is 79.1%, and when the concentration of apple leaf extract increases to 200 mg / L, the polarization resistance is 3611Ωcm 2 , the corrosion inhibition efficiency is 86.0%, when the concentration of apple leaf extract increases to 400 mg / L, the polarization resistance is 4095Ωcm 2 , the corrosion inhibition efficiency is 87.7%, when the concentration of apple leaf extract increases to 600 mg / L, the polarization resistance is 6335Ωcm 2 , the corrosion inhibition efficiency is 92.1%.

[0057] from Figure 2 (a) As can be seen, the Nyquist plot exhibits a flat semicircle in the high-frequency region and a straight line in the low-frequency region. The semicircle in the high-frequency region is generally considered to be a capacitive reactance arc, associated with charge transfer and the double layer, while the straight line in the low-frequency region represents the Warburg impedance, generally caused by the diffusion of corrosion particles or corrosion products. Therefore, copper dissolution is affected by charge transfer and diffusion processes. Compared to the blank solution, the addition of apple leaf extract increases the radius of the capacitive reactance arc in the high-frequency region of the Nyquist plot of the copper electrode, and this increases with increasing apple leaf extract concentration. This suggests that apple leaf extract can form an adsorption film on the copper surface, thereby inhibiting the charge transfer process. Furthermore, the shape of the curve after adding apple leaf extract is identical to that of the blank solution, indicating that the presence of apple leaf extract has no effect on its electrochemical properties.

[0058] At 298K, the polarization test of Cu electrode was carried out in 0.5M H2SO4 solution without and with different apple leaf extracts. The results of anodic and cathodic polarization curves are shown in Figure 2 (b). The corresponding corrosion kinetic parameters are summarized in Table 1, where E corr represents the corrosion potential, i corr represents the corrosion current density, and η represents the corrosion inhibition efficiency. c and β α are the cathode Tafel slope and the anode Tafel slope obtained by extrapolation, respectively.

[0059] Table 1

[0060]

[0061] from Figure 2As can be seen in (b), in the Cu-0.5M H2SO4 solution system, the presence of apple leaf extract causes the corrosion potential of Cu to shift negatively. On the other hand, compared with the blank solution, the cathode and anodic branches of the polarization curve in the system containing apple leaf extract shift to lower current densities, indicating that apple leaf extract is a mixed corrosion inhibitor that can simultaneously inhibit the cathode and anodic reactions of Cu in 0.5M H2SO4 solution. In addition, it can be seen from the data in Table 1 that with the increase of apple leaf extract concentration, i corr The results show that the apple leaf extract may be adsorbed on the Cu interface and form a protective film, thereby inhibiting the corrosion of the Cu electrode. corr The value is 11.25 μA cm -2 When the concentration of apple leaf extract reached 600 mg / L, the i corr down to 1.33 μA cm -2 , the corrosion inhibition efficiency of apple leaf extract can reach 87.6%.

[0062] Figure 2 (c)-(e) are scanning electron micrographs of the polished Cu sample and Cu at 298K after immersion in 0.5M H2SO4 solution with or without 600 mg / L apple leaf extract for 48 h. Figure 2 (c) is Cu before immersion, Figure 2 (e) shows that the unprotected copper sample produced large pits and cracks after being immersed in 0.5M H2SO4 solution. Figure 2 In (d), when apple leaf extract was added, the surface of copper was relatively smooth and showed only some shallow pits, indicating that apple leaf extract could inhibit the corrosion of copper under sulfuric acid conditions.

[0063] (2) Q235-0.5M H2SO4 solution test results

[0064] The obtained Nyquist plot is as follows Figure 3 As shown in (a), the impedance data of different concentrations of apple leaf extract were fitted by Zsimpwin software to obtain a series of electrochemical parameters. The experimental results show that in the blank solution without apple leaf extract, the polarization resistance is 9.604Ωcm 2 When the concentration of apple leaf extract is 100 mg / L, the polarization resistance is 42.22 Ωcm 2 , the corrosion inhibition efficiency is 77.3%, when the concentration of apple leaf extract increases to 200 mg / L, the polarization resistance is 50.63Ωcm 2, the corrosion inhibition efficiency is 81.0%, and when the concentration of apple leaf extract increases to 400 mg / L, the polarization resistance is 69.95 Ωcm 2 , the corrosion inhibition efficiency is 86.3%, when the concentration of apple leaf extract increases to 600 mg / L, the polarization resistance is 70.03Ωcm 2 , with a corrosion inhibition efficiency of 86.3%. As can be seen from the figure, the concave capacitance loop shown in the curve is related to the unevenness of the adsorbed substances on the steel surface. Compared with the blank solution, the diameter of the capacitance circle increased significantly after the addition of apple leaf extract, and the arc of the circle also increased with the increase in the amount of apple leaf extract added, indicating that the corrosion inhibitor formed a protective film on the surface of Q235 steel, which can effectively resist the erosion of corrosive particles. In addition, the shape of the curve after adding apple leaf extract corrosion inhibitor is the same as that of the blank solution, indicating that the addition of the corrosion inhibitor only increases the impedance value of the system without affecting its electrochemical properties.

[0065] At 298K, the polarization test of Q235 electrode was carried out in 0.5M H2SO4 solution without and with different concentrations of apple leaf extract. The results of anodic and cathodic polarization curves are shown in Figure 3 (b). The corresponding corrosion kinetic parameters are summarized in Table 2, where E corr represents the corrosion potential, i corr represents the corrosion current density, and η represents the corrosion inhibition efficiency. c and β α are the cathode Tafel slope and the anode Tafel slope obtained by extrapolation, respectively.

[0066] Table 2

[0067]

[0068] Such as polarization curve Figure 3 As shown in (b), compared with the blank solution, the corrosion potential of the polarization curve shifted negatively after the addition of apple leaf extract, and the anodic portion of the polarization curve nearly overlapped with that of the blank solution, indicating that apple leaf extract had no inhibitory effect on the anodic reaction of Q235 steel in sulfuric acid solution. However, its cathodic portion shifted toward lower current densities, and the shift increased with increasing concentration, indicating that apple leaf extract had a significant inhibitory effect on the cathodic reaction of Q235 steel in sulfuric acid solution. This corrosion inhibitor is a cathodic inhibitor in Q235-0.5M H2SO4. As can be seen from the data in Table 2, compared with the blank solution, the corrosion current density decreased significantly after the addition of apple leaf extract, and the corrosion current continued to decrease with increasing apple leaf concentration, indicating that the addition of the corrosion inhibitor can effectively inhibit the corrosion of Q235 steel in sulfuric acid solution.

[0069] Figure 3(c)-(e) are the scanning electron micrographs of the polished Q235 specimen and Q235 immersed in 0.5 M H2SO4 solution with or without 600 mg / L apple leaf extract at 298 K for 6 h. Figure 3 (c) is a scanning electron microscope image of the Q235 steel sheet before immersion. It can be seen that the polished Q235 steel is relatively smooth with some polishing scratches. Figure 3 (e) is Q235 steel immersed in sulfuric acid solution. It can be seen that it is highly corroded, with a large number of ridges and depressions on the surface. Figure 3 After the introduction of apple leaf extract in (d), the corrosion condition of the protected surface was significantly improved. This phenomenon indicates that apple leaf extract can play a certain corrosion inhibition effect on the corrosion of Q235 steel in sulfuric acid solution.

[0070] (3) Q235-1M HCl solution test results

[0071] At 298K, electrochemical impedance spectroscopy, potentiodynamic polarization and morphology analysis were performed on the Q235-1 M HCl solution system to illustrate the corrosion inhibition effect of adding apple leaf extract in different systems. The obtained Nyquist plot is shown in Figure 2. Figure 4 As shown in (a), the impedance data of different concentrations of apple leaf extract were fitted by Zsimpwin software to obtain a series of electrochemical parameters. The experimental results show that in the blank solution without apple leaf extract, the polarization resistance is 10.8Ωcm 2 When the concentration of apple leaf extract is 100 mg / L, the polarization resistance is 73.14 Ωcm 2 , the corrosion inhibition efficiency is 85.2%, when the concentration of apple leaf extract increases to 200 mg / L, the polarization resistance is 99.92Ωcm 2 , the corrosion inhibition efficiency is 89.2%, when the concentration of apple leaf extract increases to 400 mg / L, the polarization resistance is 136.9Ωcm 2 , the corrosion inhibition efficiency is 92.1%, and when the concentration of apple leaf extract increases to 600 mg / L, the polarization resistance is 171.3 Ωcm 2 , with a corrosion inhibition efficiency of 93.7%. As can be seen from the figure, the diameter of the capacitance arc increases significantly with increasing apple leaf extract concentration. This is due to the fact that the surface of the Q235 steel is covered by more apple leaf extract molecules, thereby increasing the thickness of the adsorption film. Furthermore, all capacitance loops show the same trend, indicating that the addition of apple leaf extract does not change the reaction mechanism of Q235.

[0072] At 298K, the Q235 electrode was polarized in 1M HCl solution without or with different concentrations of apple leaf extract. The results of the anodic and cathodic polarization curves are shown in Figure 4 (b). The corresponding corrosion kinetic parameters are summarized in Table 3, where E corr represents the corrosion potential, i corr represents the corrosion current density, and η represents the corrosion inhibition efficiency. c and β α are the cathode Tafel slope and the anode Tafel slope obtained by extrapolation, respectively.

[0073] Table 3

[0074]

[0075] Figure 4 (b) is the polarization curve of Q235 steel immersed in 1M HCl without and with different concentrations of apple leaf extract at 298K. As the concentration of apple leaf extract increases, the corrosion current density of Q235 steel in hydrochloric acid solution decreases significantly, indicating that apple leaf extract can effectively inhibit the corrosion of Q235 steel in hydrochloric acid solution. In addition, with the addition of apple leaf extract, the positions of the cathode and anode of the polarization curve both move downward, and this phenomenon becomes more significant with the increase in the concentration of apple leaf extract. However, the shape of the cathode branch of the polarization curve does not change, indicating that the hydrogen evolution process of the cathode reaction has not changed. This phenomenon may be due to the adsorption of apple leaf extract on the surface of Q235 steel, blocking its active sites, thereby reducing the corrosion of Q235 steel.

[0076] Figure 4 (c)-(e) are scanning electron micrographs of the polished Q235 specimen and Q235 immersed in 1 M HCl solution with or without 600 mg / L apple leaf extract at 298 K for 6 h, respectively. Figure 4 (a) is Q235 steel before immersion, Figure 4 (e) After being immersed in hydrochloric acid solution, the surface of Q235 steel was severely corroded and a large number of corrosion holes appeared. Figure 4 As shown in (d), after adding apple leaf extract, the surface of Q235 steel becomes significantly flat. Therefore, apple leaf extract has good corrosion inhibition performance for Q235 in hydrochloric acid medium.

[0077] (4) N80-1M HCl solution test results

[0078] At 298K, electrochemical impedance spectroscopy, potentiodynamic polarization and morphology analysis were performed on the N80-1M HCl solution system to illustrate the corrosion inhibition effect of adding apple leaf extract in different systems. The obtained Nyquist plot is shown in Figure 2. Figure 5As shown in (a), the impedance data of different concentrations of apple leaf extract were fitted by Zsimpwin software to obtain a series of electrochemical parameters. The experimental results show that in the blank solution without apple leaf extract, the polarization resistance is 34Ωcm 2 When the concentration of apple leaf extract is 100 mg / L, the polarization resistance is 279.6 Ωcm 2 , the corrosion inhibition efficiency is 87.8%, when the concentration of apple leaf extract increases to 200 mg / L, the polarization resistance is 363.6Ωcm 2 , the corrosion inhibition efficiency is 90.6%, when the concentration of apple leaf extract increases to 400 mg / L, the polarization resistance is 505.9Ωcm 2 , the corrosion inhibition efficiency is 93.3%, when the concentration of apple leaf extract increases to 600 mg / L, the polarization resistance is 518.8Ωcm 2 , with a corrosion inhibition efficiency of 93.4%. As can be seen from the figure, the addition of apple leaf extract did not change the impedance waveform, indicating that the presence of apple leaf extract does not alter the corrosion mechanism of N80 steel in hydrochloric acid solution. Compared with the blank solution, the diameter of the impedance circle increased significantly after the addition of apple leaf extract, indicating that as the concentration of apple leaf extract increases, a more complete protective adsorption layer is formed on the surface of N80 steel.

[0079] At 298 K, polarization tests were conducted on the N80 electrode in 1 M HCl solution without and with different concentrations of apple leaf extract. The results of the anodic and cathodic polarization curves are shown in Figure 5 (b). The corresponding corrosion kinetic parameters are summarized in Table 4, where E corr represents the corrosion potential, i corr represents the corrosion current density, and η represents the corrosion inhibition efficiency. c and β α are the cathode Tafel slope and the anode Tafel slope obtained by extrapolation, respectively.

[0080] Table 4

[0081]

[0082] Figure 5(b) shows the polarization curves of N80 steel immersed in 1M HCl solutions without and with varying concentrations of apple leaf extract at 298 K. Table 4 shows the polarization curve parameters for N80 steel immersed in 1M HCl solutions with varying concentrations of apple leaf extract at 298 K. It can be clearly seen that with increasing apple leaf extract concentration, the corrosion current decreases, and both the cathodic and anodic branches of the polarization curve show a downward trend, indicating that apple leaf extract can provide some protection for N80 steel. Furthermore, the shape of the cathodic branch of the polarization curve does not change with increasing apple leaf extract concentration, indicating that apple leaf extract does not alter the cathodic hydrogen reduction mechanism but effectively inhibits the cathodic hydrogen reduction reaction, thereby reducing the extent of hydrochloric acid corrosion on N80 steel.

[0083] Figure 5 (c)-(e) are scanning electron micrographs of the polished N80 specimen and N80 immersed in 1 M HCl solution with or without 600 mg / L apple leaf extract at 298 K for 6 h, respectively. Figure 5 In (a), it can be observed that the polished N80 steel surface is relatively smooth, while Figure 5 The N80 steel immersed in the hydrochloric acid solution in (e) was highly corroded, forming a large number of cracks and pits. When the apple leaf extract was added, Figure 5 As shown in (d), the corrosion degree of N80 steel is significantly reduced, and the peaks and pits on its surface become gentle, indicating that the addition of apple leaf extract can play a certain protective effect on N80 steel in hydrochloric acid solution.

[0084] (5) X80-1M HCl solution test results

[0085] At 298K, electrochemical impedance spectroscopy, potentiodynamic polarization and morphology analysis were performed on the X80-1 M HCl solution system to illustrate the corrosion inhibition effect of adding apple leaf extract in different systems. The obtained Nyquist plot is shown in Figure 2. Figure 6 As shown in (a), the impedance data of different concentrations of apple leaf extract were fitted by Zsimpwin software to obtain a series of electrochemical parameters. The experimental results show that in the blank solution without apple leaf extract, the polarization resistance is 159.2Ωcm 2 When the concentration of apple leaf extract is 100 mg / L, the polarization resistance is 312.9 Ωcm 2 , the corrosion inhibition efficiency is 49.1%, and when the concentration of apple leaf extract increases to 200 mg / L, the polarization resistance is 453.5 Ωcm 2 , the corrosion inhibition efficiency is 64.9%, when the concentration of apple leaf extract increases to 400 mg / L, the polarization resistance is 630.4Ωcm 2, the corrosion inhibition efficiency is 74.7%, when the concentration of apple leaf extract increases to 600 mg / L, the polarization resistance is 641.8Ωcm 2 , with a corrosion inhibition efficiency of 75.2%. As can be seen from the figure, the diameter of the capacitive reactance arc increases significantly with increasing apple leaf extract concentration, indicating that more apple leaf extract molecules are adsorbed on the surface of the X80 steel, forming a more complete protective film. This protection reduces active reaction sites on the metal surface and prevents charge transfer, thereby inhibiting the corrosion of X80 steel in hydrochloric acid solution.

[0086] Polarization tests were conducted on the X80 electrode in 1M HCl solution without and with different concentrations of apple leaf extract at 298K. The results of the anodic and cathodic polarization curves are shown in Figure 6 (b). The corresponding corrosion kinetic parameters are summarized in Table 5, where E corr represents the corrosion potential, i corr represents the corrosion current density, and η represents the corrosion inhibition efficiency. c and β α are the cathode Tafel slope and the anode Tafel slope obtained by extrapolation, respectively.

[0087] Table 5

[0088]

[0089] Figure 6 (b) shows the polarization curves of X80 steel immersed in 1M HCl without and with varying concentrations of apple leaf extract at 298 K. Table 5 shows the polarization curve parameters of X80 steel immersed in 1M HCl solutions with varying concentrations of apple leaf extract at 298 K. The results show that the addition of apple leaf extract reduces the corrosion currents of both the cathodic and anodic reactions, demonstrating that apple leaf extract acts as a mixed corrosion inhibitor in the X80-HCl system. Compared to the blank solution, the corrosion current of X80 steel in the apple leaf extract solution decreases by an order of magnitude, and the corrosion inhibition effect increases with increasing apple leaf extract concentration. This is likely due to the formation of an adsorption layer on the surface of the X80 steel by the apple leaf extract molecules, thereby providing corrosion protection for the X80 steel.

[0090] Figure 6 (c)-(e) are scanning electron micrographs of the polished X80 specimen and the X80 sample immersed in 1M HCl solution with or without 600 mg / L apple leaf extract at 298 K for 6 h. Figure 6 As shown in (c), the surface of the polished X80 steel is relatively smooth with only a few scratches. Figure 6 As shown in (e), the metal surface is severely corroded and a large number of groove structures appear. Figure 6 As shown in (d), after adding apple leaf extract, the corrosion condition of the X80 steel surface was significantly improved, the number of grooves was significantly reduced, and the surface became smoother. These results indicate that apple leaf extract has a certain corrosion inhibition effect on X80 steel in hydrochloric acid solution, effectively slowing the corrosion process.

[0091] Examples 2-6

[0092] 85 mL of ethyl lactate and 15 mL of anhydrous ethanol were mixed uniformly to form a solvent, and then an appropriate amount of polylactic acid-glycolic acid copolymer and the apple leaf extract prepared in Example 1 were added and mixed uniformly to form a metal preservative. The concentrations of the materials in Examples 2-6 are shown in Table 6.

[0093] Comparative Example 1

[0094] The same method as in Example 4 was used, except that the apple leaf extract was not added.

[0095] Comparative Example 2

[0096] The method of Example 4 was used, except that no polylactic acid-glycolic acid copolymer was added.

[0097] Comparative Example 3

[0098] The same method as in Example 4 was used, except that the poly(lactic acid-co-glycolic acid) copolymer and the apple leaf extract were not added.

[0099] Table 6

[0100]

[0101]

[0102] The metal preservatives prepared in Examples 2-6 and Comparative Examples 1-3 were applied to the slope of the V-groove (groove angle of 60°) of the pipe to be welded (X80 steel pipe, DN200*12.8mm). After standing for 1 month, welding was performed using the same welding process. The welded portion (weld) was then subjected to RT testing. The results are shown in Table 7.

[0103] Table 7

[0104]

[0105] As can be seen from Table 7, when the apple leaf extract and / or polylactic acid-glycolic acid copolymer prepared in the present invention is not added to the metal preservative, cracks, unfusion and porosity defects exist in the weld after the pipe section is welded. When the apple leaf extract is added but the polylactic acid-glycolic acid copolymer is not added, although the weld quality can be improved to a certain extent, cracks, unfusion and porosity defects cannot be avoided, indicating that the metal preservative in the present invention has excellent wetting and film-forming properties on the microstructure of the metal surface, and can effectively improve the welding quality of the weld slope with a microstructure.

Claims

1. A method for preparing apple leaf extract, characterized in that: The preparation method comprises the following steps: drying fresh apple leaves, crushing and sieving to obtain apple leaf powder, mixing the apple leaf powder with water, heating, filtering, and freeze-drying the filtrate to obtain apple leaf extract.

2. The preparation method according to claim 1, wherein The mass volume ratio of the apple leaf powder to water is 2-3:

100.

3. The preparation method according to claim 1 or 2, wherein The heating temperature is 333-343K and the heating time is 2-3h.

4. The preparation method according to claim 3, wherein The drying temperature is 323-333K and the drying time is 36-48h; And / or, stirring is performed while heating, and the stirring speed is 300-500 rpm.

5. The preparation method according to claim 3, wherein The method further comprises: freezing the filtrate and then performing freeze drying, wherein the freezing temperature is 255-260K and the freezing time is 12-24 hours.

6. The preparation method according to claim 1, 4 or 5, wherein The sieve aperture of the sieve is 1-1.5 mm; And / or, the freeze-drying time is 24-36 hours.

7. Use of the apple leaf extract prepared according to the preparation method according to any one of claims 1 to 6 as a corrosion inhibitor.

8. The use according to claim 7, wherein: The corrosion inhibitor is suitable for corrosion protection of metallic copper and / or carbon steel in an acidic medium; the acidic medium includes a sulfuric acid solution and / or a hydrochloric acid solution, and the concentration of the acidic medium is 0.5-1M.

9. A metal antiseptic, characterized in that: The metal preservative comprises a solvent and an additive, wherein the solvent comprises ethyl lactate and ethanol, and the additive comprises apple leaf extract and polylactic acid-glycolic acid copolymer.

10. The metal anticorrosion agent according to claim 9, wherein The volume ratio of the ethyl lactate to the ethanol is 85-90:10-15. Based on the total amount of the solvent, the concentration of the apple leaf extract is 200-600 mg / L, preferably 400-600 mg / L. The concentration of the polylactic acid-glycolic acid copolymer is 5-20 w / v; the weight average molecular weight of the polylactic acid-glycolic acid copolymer is 1000-4000.

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